飛秒雷射於透明材料加工特性之研究

Characteristics of Micromachining on Transparent Materials by Femtosecond Laser

羅紹維(Shao-Wei Luo)

指導教授 ： 蔡宏營

國立清華大學/工學院/動力機械工程學系/博士(2012年)

摘要

本論文主要研究與探討飛秒雷射加工於透明材料之特性，分別針對雷射於軟性透明材料之表面處裡、內部改質以及硬脆透明材料微加工改質後配合蝕刻之製程等三個部分進行討論。此外，為了有效掌握實驗設計所提出的改質配合蝕刻之製程方法，本研究同時利用數值計算方法擬合實驗結果，藉此了解實驗結構成形之過程，進一步決定實驗時之加工參數設定與結構設計。
在表面處理方面，主要以飛秒雷射於PET表面加工一維光柵結構，藉此提升PET材料表面之疏水特性。傳統的電漿表面改質方法，往往都具有時效性，本研究使用飛秒雷射加工之結構性疏水表面，能有效使原本親水性表面(Contact Angle, CA = 39.37o)的PET材料，大幅改善為高疏水性表面(CA = 128.47o)。
在內部改質方面，實驗利用飛秒雷射聚焦於可撓性透明材料PDMS內部，加工一維繞射光柵結構。其加工後之元件，透過二極體雷射垂直入射後，能有效產生多階繞射圖案，達到光束分光之效果。
在內部改質配合蝕刻製程方面，本研究提出一快速加工成形三角(V-Cut)微光柵之方法，實驗首先透過飛秒雷射聚焦於透明玻璃材料內部，使材料內部於聚焦點處產生鍵結破壞，利用移動平台掃描加工製作內部改質之一維光柵圖案；而後，再透過氫氟酸進行化學蝕刻成形結構。由於受改質之區域，其材料鍵結斷鍵破壞分子結構，使該區域之材料與蝕刻液反應較為迅速，因此蝕刻過程在改質區與未改質之材料間，會產生不同之蝕刻速率達到非等向性蝕刻的特性，藉此顯影成形V-Cut微光柵結構。為了拓展製程應用範圍，實驗另外設計與製作二維微稜鏡與三維光子晶體兩種結構。
在數值計算與模擬方面，本研究提出一針對雷射聚焦能量分布與材料吸收之簡化方程式，能夠快速計算飛秒雷射於透明材料內之有效改質區域範圍；了解改質區範圍後，便可透過模擬軟體設計飛秒雷射改質模型，再配合化學反應通量之模擬，計算改質配合非等向性蝕刻之結構成形過程，並且與實驗結果作比對分析。在對應的蝕刻比參數下，模擬結果之表面形貌，能確實符合實驗V-Cut微光柵結構之結果，並且進一步擬合較複雜的二維微稜鏡與三維光子晶體結構。
本論文成功地運用飛秒雷射於透明材料加工之特性，於軟性基材表面與內部進行改質處裡；另外，研究主要發展一種於透明玻璃材料進行內部改質，並且配合化學蝕刻之微奈米結構快速製程方式，同時以模擬計算方式分析其結構成形過程，藉此能輔助實驗於結構設計上之需求。

關鍵字

飛秒雷射 ； 微結構加工 ； 透明材料 ； 表面處裡 ； 改質 ； 化學蝕刻

並列摘要

Three processes of femtosecond laser machining on different transparent materials are demonstrated in this study. The characteristics of micromachining by femtosecond laser on transparent materials are discussed in three parts: surface treatment, inner modification and modification with etching process. Additionally, the numerical methods are proposed to fit the experimental results of modification with etching process.
For the surface treatment, the hydrophobic effect on the surface of flexible and transparent material, poly(ethylene terephthalate) (PET), is studied. A femtosecond laser beam is focused on the surface of PET samples for patterning micro-grating structure with different pitches to increase contact angles. The study provides a novel and effective way to control the wettability of surfaces.
For the inner modification, a diffraction grating inside a flexible polydimethylsiloxane (PDMS) fabricated by femtosecond laser direct writing is investigated. The laser beam is focused inside the PDMS substrate, and scribes in line structure. An embedded PDMS diffraction grating is successfully demonstrated based on a calculated optical phase shift structure.
For the modification with etching process, a new kind of micro-prism structures on glass substrate is fabricated. Different pitches of embedded gratings are fabricated inside glass samples by laser-induced modification firstly. Then, the glass samples are placed in hydrofluoric acid (HF) solution for structure development. The V-cut micro-prisms are formed successfully by controlling etching ratio between intrinsic glass material and laser-modified areas. To improve the process, two and three-dimension structures of microlens array and photonic crystal are fabricated, respectively.
For the numerical method on simulating the modification with etching process, a fast approach for calculating the modified volume and shape by considering the relationship between laser fluence and material absorption is proposed. The obtained structure formed by anisotropic etching between modified region and intrinsic material can be simulated for different etching selectivity. The simulated results are agreed well with the experimental results.

並列關鍵字

femtosecond laser ； micromachining ； transparent material ； surface treatment ； modification ； chemical etching

參考文獻

[1] W. M. Steen, and J. Mazumder, "Laser Material Processing," 4th, 2010, pp.12.

[3] O. Svelto, "Principles of Lasers," 5th, 2010, pp.318-321.

[4] E. Hanamura, Y. Kawabe, and A. Yamanaka, "Quantum Nonlinear Optics," 2007, pp.102.

[5] R. R. Gattass, and E. Mazur, "Femtosecond laser micromachining in transparent materials," Nature Photonics, vol. 2, 2008, pp. 219-225.

[6] S. K. Sundaram, and E. Mazur, "Inducing and probing non-thermal transitions in semiconductors using femtosecond laser pulses," Nature Materials, vol. 1, 2002, pp. 217-214.